Well you could have someone visit your world with Frostner and slap Bonemass silly with it. Then you could send them back to their home world with a couple stacks of iron or something.

And yeah, just staying above him and shooting him is viable; he has pretty much no way of getting you up there. The minions he spawns do have bows sometimes though. But keep in mind that he has a very high resistance to piercing damage which is what bows do. I suggested the frost arrows because they do bonus damage to anything that's wet and the swamp is always wet.